This invention relates to the attachment of friction linings to backing plates, as may be utilised in vehicle or other machine braking systems, clutch mechanisms, or other mechanisms where friction linings are to be attached to a backing plate.
For the purposes of this specification reference will be made mainly to the attachment of friction lining segments to sole plates of brake shoes for vehicles, particularly heavy duty vehicles such as trucks and buses which because of their weight and the terrain in which they may be required to operate, must have secure attachment of the friction linings on the brake shoes to avoid brake malfunction and the consequences resulting therefrom. The invention is also applicable to other vehicles such as cars, motorcycles, trains and aeroplane braking systems, and clutch mechanisms where applicable, as well as other machinery where brake or clutch mechanisms may be necessary, including elevators.
Conventional attachments between friction linings and braking plates, such as between brake linings and sole plates in brake shoes, have involved the use of rivets coupling the linings to the backing plates. The heads of the rivets on the lining side of the attachment are received in recessed holes, and maintain attachment until such time as the friction linings wear away to an extent that the rivet heads and an associated braking surface, such as a surface of a brake drum or brake disc, become sufficiently close as to require replacement of the friction linings. One well known problem with such attachments is that there is a build up of grit in the recesses for the rivets which as a result of the rubbing action of the linings against the associated braking surface causes scouring or other damage to the braking surface requiring machining maintenance from time to time to repair the damage to the brake drum or disc. In addition, in order to securely attach the linings to the backing plates (sole plates) a considerable number of rivets may be required which adds to the expense, both in parts and labour, in manufacturing and maintaining the brake, clutch or equivalent component.
An alternative attachment is also known using direct bonding of the linings to the backing plates without the necessity for rivets and using hot or cold bonding agents which because of the advances in bonding agent technology have allowed for reliable attachment in most instances. However, in some heavy duty applications, such as braking systems for trucks, and more particularly buses where safety factors are more critical, there are perceived problems in relation to detachment of the friction linings (brake linings) from the backing plates (brake soles) and although brake failures resulting from such detachments are very rare, there is some concern on the part of truck and bus operators to utilising bonded brake linings in such severe service applications. The likely main cause of brake malfunction with bonding techniques is that as a brake lining becomes worn, and as a result thinner, heat generated during braking operations is more rapidly conducted to the interface between the lining and the backing plate whereby the hot or cold bonding agent can be adversely affected to the extent that its bonding action breaks down and the lining separates from the backing plate.
In the past it has been proposed to provide an attachment between a friction lining and a backing plate, in which the lining is keyed to the backing plate by one or more keying elements attached to the backing plate and cooperating with one or more associated grooves in the lining in such a manner as to prevent the lining from being detached from the backing plate.
One such attachment is disclosed in Australian patent specification no. 149358 entitled xe2x80x9cimprovements in or relating to a clutch of brake mechanismxe2x80x9d. However, such proposals have involved the use of keying elements which extend completely across the backing plate, as do the associated grooves in the lining, thus leading to the possibility that the lining may move laterally of, or even off, the backing plate under certain circumstances.
It is therefore an object of the present invention to provide an attachment between a friction lining and backing plate which eliminates, or at least minimises, the above problems with known riveted, bonded, or keyed and groove attachments, and in particular with regard to the latter any possibility that there will be relative lateral movement to any large extent between the lining and the backing plate.
In accordance with the present invention there is provided an attachment between a friction lining and a backing plate, in which the lining is keyed to the backing plate by a plurality of keying elements attached to the backing plate and cooperating with a plurality of associated recesses in the lining in such a manner as to prevent the lining from becoming detached from the backing plate, and wherein at least one of the keying elements and its associated recess is such that one side or end thereof terminates within the lining material laterally of the lining, whereby there will be no, or a limited amount of, relative lateral movement between the lining and backing plate.
In one embodiment at least some of the keying elements are elongate and received in correspondingly elongate grooves and at least one of those keying elements and associated groove extends only partially across the interface between the backing plate and friction lining from one side thereof, and at least one other of those keying elements and associated groove also extends only partially across the interface from the other side thereof.
In another embodiment at least some of the keying elements are suitable shaped elements received in recesses residing totally within the lining material.
Preferably the keying elements are attached to the backing plate by screws, bolts or rivets extending through apertures in the backing plates and into the keying elements after the lining has been positioned on the backing plate.
Alternatively the keying elements may be attached by bonding or gluing them within the respective recesses.
In a still further alternative embodiment the attachment may be formed by a combination of screws, bolts or rivets and bonding or gluing.
In a still further alternative embodiment the keying elements may be moulded into the lining material at the time of moulding of the linings.
Possibly a bonding agent may also be provided between the lining and the backing plate to enhance the attachment of the lining to the plate.
The invention also envisages a friction lining having at least one keying element.
The invention also envisages a friction lining with at least one recess and a keying element for association therewith.